Following and recording



May 31, 1949. '1 w. J. KlNDERMA N 2,472,019

FOLLOWING AND RECORDING Filed Aug. 29, 1946 9 Sheets-Sheet 1 J i :3 FaLLow M H 070R 5 k -ec'rRoN It. Tammi Com-Rm. UN IT 35 CONTRULVANE flx/s or Fol-4 7M CoNTR'oL VAN 64 PHOTOTUBE INVENTOR d d 44 7/ m mum nnrutwu; tM YlUYF aixxoss REF 1 2 5 0 2 O 3 ERERCE EXAMINER y 1949. w. J. KINDERMAN 2,472,019

FOLLOWING AND RECORDING Filed Aug. 29, 1946 9 Sheets-Sheet 2 4X16 oFfar/rmn' InPuFl 84 w CONTROLVANE fi! a0 a I I v 82 a I LIGHTBEAI'I EXAMINER REFERENCE 9 Sheets-Sheet 3 Filed Aug. 29. 1946 a W a a 0 V a 1 M 2 w m 0 Q J N a W "m 0 M 0 J, w i Z 4 E q a 5 an A i fiw a 4 J m 0W & W a o 5 w w w w x G A s AMPLIFIER AND Powcqsoul cn INYENTOR ATTORNEYS AF'FI-IF'IEK AND POWERSQQRQE.

May 31, 1949. w. J. KINDERMAN FOLLOWING AND RECORDING 9 Sheets-Sheet 4 Filed Aug. 29, 19 46 INVENTOR EXAMINER J3 REFERENCE y 1949. w. J. KINDERMAN 2,472,019

FOLLOWING AND RECORDING:

9 Sheets-Sheet 5 Filed Aug. 29, 1946 INVENTOR Wxljfnakrman EXAMlNER 3,5 0 5 2 0 3 Us REFERENCE W. J. KINDERMAN FOLLOWING AND RECORDING May 31, 1949.

Filed Aug. 29, 1946 9 Sheets-Sheet 6 INVENTOR maid 2 5 0 2 0 3 CROSS REFERENCE EXAMINER y 31, 1949- w. J. KINDERMAN 2,472,019

Filed Aug. 29, 1946 i I E 9 I 4 2 5 .20 3 CROSS REFERENCE m m I May 31, 1949. w. J. KINDERMAN 2,472,019

FOLLOWING AND RECORDING i Filed Aug. 29. 1946 9 Sheets-Sheet a I (I 55 Patented May 31, 1949 UNITED STATES? PATENT OFFIQE- FOLLOWING AN D RECORDING Walter J.' Kinderman' Philadelphia; Pa., assignorto Yarnall-Waring-.Company,- Philadelphia, Pa., a corporation of Pennsylvania Application August 29, 1946; Serial No; 693,795

great accuracy in reproduction 'ofthe motion ofthe primary indicator, and marked simplifica-' tion in the equipment required.

'A-"further'purpose is-to produce a follow-up mechanism which can be applied to existing'pri mary indicators without the necessity of any marked change in the primary indicators.

A-further purpose is to obtain reasonably high' speed response,'by thefollow-up-"mechanism, to change in the position of the primary indicator;

A further-purpose is to-make availablein the follow-up mechanism ample force to operate any auxiliary equipment such as alarms, controllers; or th'e'likewithout the possibility of imposing a force reaction on the primary indicator.

Afurther purpose is to' produce a device which is comparatively insensitive to calibration of phototubes employed.

A further purpose is to produce a device which will permit the recorder to move conveniently to limiting positions, suitably an off" position and aposition for changing the record.

A further purpose is to" employ a primary indicator having angular movement, a followup element having angular movement, prefer-' I ably on the same axis as the primary'indicator and generally'conforming to that'or the primary indicator, means for producing a beam of light which moves with the follow-up element and is preferably mounted thereon, means such as a-vane on the primary indicator for variantly eclipsing the light beam in accordance with the relative angular position of the primary indicator and the follow-up element, and phototube means for continuously angularly shifting the follow-up element as the primary indicator shifts angularly and in response to the extent of the eclipsing of thebeam.

A further purpose is to employ, on the primary indicator, means for cutting the beam of light in onerelative angular position, with respect to the follow-up element, for clearing the beamin another relative angular pwition and for par-'- tially cutting the beamin an intermediate relative angular position, in combination with a phototube responding to the quantity of light, if anin'passing in-th'e' beam, a power source for the phototube, an amplifier for the phototube, means for providing a counter-torque on the folssiciaims- (ciw- 2 low-up element and a motor driving the follow-up element against the counter-torque in continuous response to the amplified output of the photoetube.

A further purpose in instruments of the character mentioned is to employ phototubemeans for maintaining the primary indicator and the fol low-up element in the relation of equilibrium'irr which .the beam is partially out.

A further purpose is to control the follow-up in response to the quantity of light in order to restore equilibrium conditions of initial illumination.

Aiurther purpose is touse a single straight direct beam of light for control of the follow up element.

A furtherpurpose is to mount both the light source and the-phototube on the follow-up element, with one nearer to the axisof rotation than the other,'and the vane between, preferably placing the light source farther from the axis than the phototube, and placing the phototube on the opposite side of theaxis from the light source.

A further'purpose-is to employ a sheet metal vane having considerable radial length.

A further purpose is to locate the'phototube out of the line of centers between the light source-and the axis, whereby the photoelement in one position of the vane may receive the full beam of the light.

A further purpose is to employ a light cut-oi! surface on the vane which excludes a portion of the beam at all times, in cooperation with a vane which selectivelyeclipses the light.

A further purpose is to use a segmental vane describinga circumferential path.

A'further purpose is to employ a vane in a plane perpendicular to the axis.

A further purpose is to control the following by double photoelements.

A further purpose is to operate a recorder to a limiting position in which the pen is removed from'the' record by means of the follow-up. mechanism.

Further purposes appear in the specifications and inthe claims.

In the drawings I have chosen to illustrate a few only of the embodiments of my invention, the forms shown being chosen from the standpoints of convenience in illustration, satisfactory operation and clear demonstration of the'principles involved.

Figure 1 is a diagrammatic perspective of the preferred embodiment of my invention.

Figure 2 is an enlarged diagrammatic elevation of a portion of Figure 1, showing the relations between the light source, the phototube and the vane in one position.

Figure 3 is a view similar to Figure 2, taken in another position.

Figure 4 is a view similar to Figure 2 in a still different position.

Figure 5 is a diagrammatic perspective of a variant embodiment of the invention.

Figure 6 is a diagrammatic perspective of a still different form.

Figures 7 to 9 inclusive are fragmentary diagrammatic elevations showing the light source,

the phototube and the vane in various positions of the structure of Figure 6.

Figure 10 is a diagrammatic perspective showing a further variation.

Figure 11 is a diagrammatic perspective of an embodiment using double photoelements.

Figure 12 is a plan of a recorder and follow-up mechanism conforming with the invention, and employing the structure of Figures 1 to 4 inclusive, with a placement view of a water level gauge attached.

Figure 13 is a front elevation of the mechanism of Figure 12, omitting the cover from the recorder, but adding a water level gauge in front elevation.

Figure 13 is a fragmentary enlarged section of Figure 13 on the line |3'-.-i 8

Figure 14 is a rear elevation of the form of Figures 12 and 13, omitting the rear portion of the case.

Figure 15 is a right end elevation of Figure 12, omitting the liquid level gauge except for the control vane.

Figure 16 is an enlarged fragmentary perspective of the follow-up mechanism shown in Figures 12 to 15 inclusive.

Figure 17 is a detail top plan view of the primary indicator of Figures 12 to 16.

Figure 18 is a circuit diagram.

Figure 19 is a more detailed circuit diagram which may conform with Figure 18.

Figure 20 is a variation of Figure 19.

Figure 21 is a variant circuit diagram for a capacitor type induction motor.

Figures 22 to 24 inclusive illustrate variant circuit diagrams for use in connection with the form of Figure 11.

Like numerals refer to like parts throughout.

Describing in illustration but not in limitation and referring to the drawings:

In the prior art, following mechanisms have been employed for reproducing the motion of a primary indicator, but in the main they have not been widely applicable because of the complicated mechanism, the necessity of making radical and often unacceptable changes in the pr mary indicator, and in some cases because of imposition of drag or other force reaction on the primary indicator.

It will be understood that wherever a primary indicator is referred to, it may be any suitable member of an instrument which moves in response to variation in a quantity or quality being measured, determined or indicated. In the present case the primary indicator will normally be a pointer, scale arm or other indicating element, preferably of a boiler or other suitable water level indicator, but suitably of some other device indieating some different quantity such as flow, volume, pressure or the like. The primary indicator may also merely indicate a reference angle 4 such as azimuth, elevation or some reference angle used in levelling or surveying.

By the present invention it is possible to follow a primary indicator with very high accuracy, without imposing any drag, friction or other force reaction on the primary indicator. Since the operation is entirely by intersection of a light beam, it will be evident of course that this can be accomplished without any interference with the operation of the primary indicator, The present system is capable of response with considerable speed, the minimum speed of response in one desirable embodiment being about one second for movement from end to end of the instrument scale.

The device is extremely simple and normally does not necessitate bending of light beams and aligning of beams progressing at various angles. The controlling factor to which the device responds is change in quantity of light, and the device is comparatively little affected by normal change in calibration of phototubes. When photo tubes are mentioned, any suitable photosensitive electronic tube is included.

In order to app y the follow-up mechanism of the invention to existing primary indicators, it is not necessary to make any radical change in such existing equipment. Ample force is provided in the follow-up system to operate auxiliary equipment such as high-low alarms, level controllers or the like, entirely without reaction on the primary indicator. The follow-up mechanism itself may be used to perform auxiliary functions.. such as moving the recording pen to an 01? position or to a limiting position for changing the record.

Referring to the form of Figures 1 to 4 inclusive, the primary indicator 30 consists of a pointer 3i moving on an axis 32. over an angular path indicated by the arrow 33, and suitably counterweighted at 34, While the primary indicator may move over any desired arc greater or lesser than a circumference, the device is intended to be applied in the forms shown to an application having a range of movement of the order of 100.

In order to aid the function of following the primary indicator, the primary indicator is provided with a control vane 35 suitably mounted at 38 on the pointer.

In the preferred embodiment the control vane suitably consists of sheet metal extending radially of the primary indicator, having considerable radial length and very little thickness. cut 0!! at the outer radial and at 31, and terminating at the inner radial end at 3| in line with the axis 32. While in the form shown the vane 35 is likely to be a special vane designed for the purpose and applied to the primary indicator, it will be understood that in many cases a surface of the primary indicator existing prior to the installation of the follow-up system may be used to serve the follow-up function. For example where location and dimensions permit, a portion of the head 38 of the pointer arrow may serve this purpose. In any case the installation of a vane 35 on the primary indicator can readily be accomplished in most instances without seriously impairing the structure of the primary indicator and usually with mere necessity to change the counterweighting.

As previously explained, the primary indicator may respond to any suitable impulse measuring or indicating some quantity or fact in respent to any of a wide variety of attributes, but in the preferred embodiment it is desirable that the axis shaft 32 be the shaft of a water level indicator of the type shown at II in my United States Patent application, Serial No. 517,242, filed January 6, 1944, for Differential pressure gauge. The disclosure of this application is incorporated herein by reference and made a part hereof.

The follow-up mechanism includes a followup element 40 comprising an arm 4| suitably pivoted at 42 On an axis, which is preferably, although not essentially, the same as the axis 32 of the primary indicator. If any differences between the axes exist, however, the results will be much more complicated, and therefore it is decidedly advantageous to have the axes 32 and 42 coincident, as shown. Preferably mounted on and moving with the arm 4|, I provide a co-opcrating light source 43 and phototube 44, respectively at different distances from the axis, on either side of the vane 35, and preferably one near the radial outer end of the arm 4| and the other at the opposite end thereof adjacent the axis, as shown.

I find that the sensitivity of the device is considerably increased by locating the light source at the radial outer end remote from the axis, and locating the phototube nearer the axis. This is true because a large amount of eclipsing of the light is accomplished by a small movement of the end of the vane when, as shown, the moving end 3! of the vane is close to the light source.

In order that the device may function properly, it is important that the vane 35 be between the light source 43 and the phototube 44, so that the vane can control the passage of light from the source to the phototube.

The light source is preferably an electric incandescent lamp 45 mounted in a socket 46 and lighted by electrical connections 41. Surrounding the lamp is a metallic cover or shield 48 provided with a preferably narrow rectangular slit 49 which is suitably directed toward the axis in a general radial direction in this form.

It has been found that the most effective light source is a thin diverging flat ribbon light beam which travels in the general direction of the vane in equilibrium position. The narrow slit in the lamp cover provides a simple way of securing this beam.

For best results the slit in the lamp cover should be located as near to the light source as practicable, and the slit should be as narrow as possible consistent with full illumination of the phototube element by divergence of the beam. The adjoining end of the vane should be close to the slit, and this provides for sharp cut-off of light by the control end 31 of the vane with minimum movement of the vane, resulting in a very sensitive response. The controlling end of the vane will preferably be substantially closer to the slit than one-half of the length of the vane.

The phototube has a photoelement or cathode 50 and is mounted on a socket having electrical connections 52 to an amplifier.

-In order to drive the mechanism and produce the required follow-up, I provide a follow-up motor -53 having a shaft 54 carrying a pinion 55 which is intergeared with a gear (actually in this case a segment) 56 on the shaft 42. The light source 43 is supplied with power, and the motor is operated in accordance with the amplified impulse from the phototube, by an electronic torque control unit or amplifier 51 connected by a suitable flexible cable 58 to the lamp and phototube and by a suitable cable 59 to the motor, and recalving power from asuitable soiu'ce at 80, preterably of alternating current at 60 cycles and 119 volts.

The follow-up motor 53 is actuated as later explained in response to the quantity of light picked up by the phototube, and is preferably a torque motor which has substantially zero torque when the quantity oflight received by the phototube -is substantially zero and a maximum torque when the quantity of light received by the phototube is a max'nnum.

Although the motor 53 may be either of the alternating or direct current type, and if alternating may be either of the conventional type or a. special type, in the preferred embodiment as shown in Figure .l, the followup motor is preferably a capacitor type squirrel cage induction motor, which is :in itself well known in the art.

Where a capacitor motor is'employed, any-suitable capacitor type indnction motor maybe used. In a motor of this type, the direction of rotation is determined by the direction of phase displacement, and the motor is a two-phase motor in the sense that the :motor itself is :operating on two different displaced phases, although a two-phase power source not required. Any other twophase motor may be used with a two-phase power source if desired. One suitable type of capacitor induction motor is the drag cup type, well known in the art.

Instead of actuating the follow-up element by direct drive on the motor shaft, it will be noted that gearing at 55 and 56 has been interposed, permitting the use of a smaller motor with mechanical advantage from the gearing and permitting reduction in the cost and power of the electronic torque control unit, without serious sacrifice of the speed 'ofresponse.

As later explained, the motor 53 drives in only one direction, and is :opposedby a counter-torque on the follow-up mechanism. In the preferred embodiment the counter-torque is provided .by gravity acting in unbalanced relation on the fob low-up mechanism. Thus if the drive of the motor 53 isin the direction to turn the segment 56 and the follow-up element counterclockwise as shown by the arrow '6l, the counter-torque applied by gravity will be clockwise or in the direction of the arrow 62. While gravity pro vides the preferred .form of counter-torque, in Figure 10 I illustrate counter-torque applied by a spring, and in other devices I show electrical means for applying counter-torque.

The counter-torque will be substantially less than the maximum available torque, and substantially greater than the friction in the mechanism. It is often desirable to maintain the counter-torque at about one-half the torque on full motor operation.

Referring particularly to Figures 2 to 4, it will be noted that in each of these figures the phototube is not located in the line between the axis and the light source, but .is preferably deliberately placed out of this line. While, if desired. the phototube may be in some other position with reference to the light source, it is preferred to locate it on anextension 63 of the arm 4| on the opposite end of the arm-from the light source and beyond the axis '42. Not only is the phototube beyond the axis, but it is preferably out of the line between the axis and the light source as well shown in Figures 2 to 4. Thus in these forms, 'if the coincident axis is at '32, 42, and the center of the filament 54 of the lamp I5 is at '65, the light beam 86 is preferably directed so that, taking account of its divergence at 61, it will fully illuminate the photoelement 50 of the phototube 44, missing the vane 35, when the vane is in the clear position as shown in Figure 2. In other words, in this form the line from the center 65 of the light source to the center 68 of the phototube extends to one side and in this case below the axis, and the outer edge 69 of the light beam nearest to the axis is permitted in the clear position of the vane to contact the limiting edge of the photoelement SI.

Thus it will be evident that since the edge ll of the photosensitive element (cathode) 50 is closest to the pivot oi the vane, the side of the photosensitive element adjoining the edge 10 will be most frequently cut ofi by the vane, while the side adjoining the opposite edge II will be less frequently obscured.

Thus it will be evident that in the preferred embodiment shown in Figures 1 to 4 inclusive, one edge 10 of the phototube element, rather than the center of the phototube, is brought into approximate alignment with the line of centers between the axis and the center of the light source.

This construction has the advantage that there is no possibility of the phototube receiving light from both sides of the vane, and a long thin sheet metal vane, without other structural complication, is permitted, while at the same time, since the lever arm of the vane from the pivot is so long, the follow-up mechanism is very sensitive to slight changes of the angular position of the vane, since they produce very marked valving or eclipsing of the light. At the same time it will be evident that the location of the outer end of the vane closest to the light is preferable because a slight change in the angular position of the vane produces a very marked change in the eclipsing, since the beam is at its very narrowest point at the slit where it issues through the cover 48. The reverse arrangement with the phototube upon the outer end of the follow-up element is markedly less sensitive since the outer end of the vane is acting on the light at a point where it is widely diverging, as shown by the beam in Figure 2, which enters the phototube. Because of these advantages, as well as the great simplicity, low cost, reliability and low maintenance, the form of Figures 1 to 4 utilizing gravity counter-torque above referred to is considered to be preferable.

In operation of the form of Figures 1 to 4, it will be evident that the vane and follow-up mechanism will reach an equilibrium position somewhat as shown in Figure 4. It now the primary indicator moves counterclockwise, causing the outer end of the vane to move up into the position of Figure 2, the efiect is to completely free the light beam 66 from the eclipsing effect of the vane 35, greatly increasing the amount of light reaching the phototube element 50. Increase in the amount of light reaching the phototube element increases the electric impulse passing from the phototube to the electronic torque control unit 51 and increases the amplified impulse leaving the unit 51 and passing through connections 59 to the motor 53. Since the efiect of the motor is to drive the follow-up element 40 in the counterclockwise direction, as shown by the arrow 6|, the follow-up mechanism will be driven by the motor counterclockwise following the motion of the vane and will stop, as later explained, when equilibrium is restored.

It will be understood that at some intermediate position of illumination, as shown in Figure 4, the amplified impulse from the phototube when applied to the motor will produce just enough torque to overcome the counter-torque, in this case applied by gravity to the follow-up mechanism. Therefore, when in Figure 2 the illumination of the phototube was increased, the amplified impulse from the phototube was accordingly increased and the torque increased to full torque, substantially in excess of the counter-torque applied by gravity or otherwise, thus permitting the follow-up motion which is described in Figure 2.

Let us now assume that the motion oi the primary indicator and of the vane is clockwise, as shown in Figure 3. The effect is then to eclipse or cut ofi the beam 66, as shown at 12, so that substantially no light reaches the phototube. The phototube impulse will then accordingly be cut off, or dropped to a low threshold value, so that the amplified impulse will not produce suflleient torque in the motor to overcome the countertorque applied by gravity or otherwise. Accordingly, the counter-torque will exceed the torque and cause the follow-up mechanism to move clockwise in the direction of the arrow 62 (Figure 3) which again tends to restore coincidence between the follow-up element and the primary indicator.

However the motion starts, whether as a clearing motion or an eclipsing motion with respect to the beam, the final equilibrium will be attained as indicated in Figure 4 when the beam is partially eclipsed, as shown at 13, in which the upper portion H of the beam is cut oil and the lower portion 15 of the beam is cleared. In this condition the phototube impulse when amplified is just sumcient to produce a torque in the motor which overcomes the counter-torque, and therelui'e equilibrium will be maintained in this position so long as the primary indicator remains stationary.

Whenever the primary indicator again begins to move, the action of Figures 2 or 3 will be repeated dependin upon direction of motion, with a view to restoring coincidence between the primary indicator and the follow-up element.

It will be understood, of course, that the conditions of complete clearing and complete eclipsing shown in Figures 2 and 3 are extreme conditions, which can only occur in the case of extremes of motion oi. the primary indicator in one or the other direction, and that actually in normal operation there will be momentarily minute motions of the primary indicator which will cause minute changes in illumination of the phototube element, with minute follow-up motion, but after the manner indicated in Figures 2 and 3.

It will thus be evident that the angular movement of the primary indicator can be reproduced perfectly by the angular movement of the followup element. The control is entirely by the degree of eclipsing of the light beam by the vane, or in other terms, the change in the quantity of light on the photoelement of the phototube, which tends to restore the initial illumination conditions and recreate equilibrium.

It will be evident that in this and a number of other forms of the invention, the amplified output of the phototube continuously urges the follow-up mechanism in one direction, but the question of whether or not motion in that direction occurs depends upon whether or not the counter-torque is overcome iby' the :amplifledphototube impulse cacting'on the motor.

It will be evident that infilgureszto 4, the light beam deviates slightly from the radial direction, but may be regarded as -being generally radial, one edge -;of the beam being'truiy-radial.

In the form of Figure '5, the structure differs slightly from that of Figures '1 to 4. In this form the primary indicator 3!! has'been slightly modified to show an ofiset end lfi carrying thehead 39.

'To indicate conveniently that the primary indicator 'may be part of a water level system, I :show at the end of the axis shaft *32 an arm l-I carrying a float 18, intended to be inside a vessel such as a boiler to indicate the'liquid leveltherein. At some point such as I 9, the motion-ofthe float is transmittedby any suitable-meanssuch as that described in my copending application above-re- -.ferred to, or'by a conventional stufling box or rotating joint, through the wall of the boiler -or -through the vessel, not-shown.

The vane construction has been slightly varied in this form to show an extension 3t on one side 'of the vane, which is attached to the pointer and avoids'the necessityof using the rod at 36, as shown in Figure 1.

In this form of the invention the light beam is placed truly radially with respect to the coincident axes 32, 42 of the primary indicator and the follow-up element. "Thus the center of the .photoelement 50 of the p'hototube 44 is on the line of centers between the axis "and 'the center of the light source. This presents the problem, *where a very light, thin'sheet metal vane of con- ;siderable axial length is used, as shown, of preventing the possibility that the beam will be divided at the center-and light from both sides of the beam might reach-the photoelement, thus "confusing response. To prevent this possibility, alight cut-off surface =80 has been located at a convenient point on the wane, preferably at the :axis, and extending transversely to the 'beam'for a sufficient distance to-cut :ol'f an rays which might pass to the phototube over the top of the wane in any operatingposition of the vane. Thus in this form, theupperlportion of the phototube element 59 adjoining the edge 10 :is-substantia'lly inactive and the device operates by variant re- 'sponse from the quantity of light reaching the vlower portion of the .phototube element. 'While this arrangement :is operative, it is inefiicient since it doesnot employ :the zDhObOtllbfi element to best advantage.

In the structure of 'Figure 5 the follow-up ele- -.-ment 40 i incorporated with the segmental 'gear :56 as a single member 781, reducing the number (of component parts. In the previous piorm shown, the vane 35 was 'extended in a radial direction, but 'it will'be evident that other vane contoursand directions may be employed with or without change in the direction of the beam.

In Figure '6. the vane 35' is extended circum- -.erentially with respect to the axis 32 of the primary indicator 3!], being :suitably mounted on the pointer at 82, and extending in segmental form from a top-edge 83 to a bottom controlling edge 84. The counterweight '34 has been broken away in this form and-in'that of Figur 10. The :light source 43 and the .photo tube '44 are prefer- .ably radially-spacedas in the forms previousiy described, and are located one immediately radially beyond and the other immediately radi- -'ally within the vane 35'.

Depending upon theoperation of the primary indicator, 'the vane may =be-shortened 'or may "require lengthening in respect to its circumferen- -tial extent, as it is obviously important that the characteristics of-the device should'not permit 5 "wide enough displacement betweenthe primary indicator and the follow-up element, sothat confusion-could occur'between the control edge m4 and theopposite edge-83 of the vane. In all "of "the forms shown, it is-contemplated'that the pri- -l 0 mary indicator and the-follow-up device willhave limited arcuatemotion, butit will be understood,

of course, that'this is not-essential and the principle may be applied with movement of a complete circumference or complete circumferences. However. where limited arcuate'motion is employed, it will be convenient to'extend the-vane 35 over a substantial portion of the range "of arcuate movement.

-The operation will be essentially the same as in the other 'forms. Thus if the Primary-indicator moves counterclockwise in Figure '7. ithe light beam from the "light source tothe photo- 'tube -is completely clear'and the amplified impulse from the phototube "drives 'the motor 13 "in a direction to turn the follow-up mechanism -:counterclockwise in the direction of the arrow .6l to restore equilibrium and coincidence between the primary indicator and the followup mechanism.

Likewise if the primaryindicator moves:clo'ckwise, as shown in Figured the vane-' eclipses 'the beam, causing the amplified phototube impulse to drop off "to practically =zero, :-so that the counter-torque prevails over the torque of the :motor 58 and the foliow-up-element 40 moves vclockwise in'IligureB insthe directionof the arrow n to restore coincidenceand equilibrium. The

equilibrium condition, :as shown in Figure '9, 'is

that in which "the beam is :partially split by the 4) controlling-edge of the-vane, and in'that 'condition the predetermined coincidence exists and the recorder or other device operated by the fol- :low-up mechanism will agree with "the primary indicator.

:In the form of Figure -10,:the -vane35 is positioned in a plane 'atrightzangles tothe axis 32 of the primary indicator .30, 'andthe follow-up :element 40 is t'formed-as an arm :85 transverse to thesegmental vgear 56. The light source-43 and .1 the phototu'be'fl are located as-close together as convenient on the "arm =85, one on either side of the vane 35*. The controlling edge of the vane in this case is at 84 and the :operation is the same as that already described in the other :forms.

In this form of the invention a spring counter- '-:torque-is provided at 86 on the axis shaft '42 -01 the follow-up element, in this case replacingthe action of gravity used in the earlier forms.

As shown in Figure 1-1, Imay, in some cases, use a twin phototube or two phototubes, preferably having two separate 'phototube cathode elements in-one envelope, :as shown at '81, 88, with the vane'35 located radially and centering at the center of the beam so 'that in-equilibrium position light will' be suppliedto each element and ":88 from the light-source, and in e'fiect'the energy imparted from the amplified impulse of one =or the other photoel'ement will act as-a countertorque. In this "form the motor 53' will be reversing, preferably 'a capacitor type induction .motor. The devices of Figures 22 to '24 inclusive :are suitable-to operate thisiievice.

It will :be understood that in Figm'e 11 "the operation is substantially the same as in the other forms, but with the marked difference that when the vane moves in the direction to eclipse the portion of the beam reaching one photoelement, the amplified impulse from the other photoelement may remain unchanged if the control vane is accurately out of the path of the beam to the other element when the vane is centered or may be slightly increased if the movement of the control vane allows slightly more light to come to the photoelement not being eclipsed. Thus the torque mechanism or motor winding responding to the photoelement not being eclipsed will act as a substantially greater torque to move the follow-up element in the direction to follow the primary indicator.

Figures 12 to 17 inclusive illustrate a more complete embodiment of the invention based upon the form of Figures 1 to 4 inclusive, suitably consisting of a liquid level indicator 89 and a recorder combined with follow-up mechanism of the type described.

The liquid level indicator may be of any suitable type, for example connected to a float as diagrammatically suggested in Figure 5, and having primary indicator on a common axis 32 with the follow-up mechanism. The vane is of the type shown in Figure 1. The head 39 of the pointer is, in the preferred embodiment, suitably enclosed by a cover 9| having a cover glass 82 provided with indications 83.

The follow-up element includes an arm I mounting the light source and the phototube in the relation indicated in Figure 1, the phototube being on the opposite side of the axis from the light source and the vane controlling the beam passing from the light source to the phototube. The arm 4| is secured to the segmental gear 56 by a bracket 94 fastened at 95 to the gear and at 96 to the arm. The mounting of the phototube is aided by a clip 91 extending over the top of the phototube and secured to the arm as shown in Figure 16.

A rack 98 is movable up and down in guides 09 and I00, supported on the end IOI of the case I02 of the recorder 90, and the rack is intergeared at I03 with the segmental gear 55. The end of the rack is bent at I 04 to form a flange I05 to prevent movement beyond the guides. At the upper end of the rack a reverse bend extension I06 over the guide I00 carries a pen arm I0'I which is bent at I08 and extends through a slot I09 in the front IIO of the recorder, suitably extending across the face of a rotatable recording disk III carrying a graduated chart II 2 of any conventional type. Apen is located at I01. The

recorder has a radial inner limiting pen position II 3 corresponding with an off position of the device and a radial limiting outer-position H4, specially adapted for changing the chart, in which the pen arm I01. of suitable resilient metal, is raised from the surface of the chart II2 by encountering a pen lift cam I I5 sloping from a minimum at II 5' where it is first encountered to a maximum at H5, in the pen lift position. This structure is illustrated in Figure 13a.

It will be evident that an important feature of the invention is the ability to employ the power of the follow-up mechanism to move the recorder to the upper and lower limiting positions for the special purposes of indicating an off position, as when the power fails, and for moving to an upper limiting position for changing the chart.

As already explained, an important advantage of the device of this invention is that ample power is available in the follow-up mechanism to per- Cal form auxiliary functions, such as operating highlow alarms and level controllers, without drag on the primary indicator. To suggest this I show in Figure 13 electric switches IIS and Ill respectively for an electric high and a low level alarm and controller, of any well known type, suitably a push button with a hemispherical top, closed by the pen arm when it reaches the switch position, and otherwise open.

The recorder may be of conventional type in respect to other features, and is shown including a chart turning shaft I I8, a chart rotating motor. suitably a timing motor, H9 having electrical connections I20 to a suitable power source. The interior of the recorder and the face are suitably illuminated by lamps III (the front H0 is desirably made of translucent or transparent material such as acrylic resin so that the illumination will be applied to the chart), connected to a power source at I22 and controlled by a switch I23. The amplifier and power connection, or electronic torque control unit 51 is desirably built into the recorder case, and provided with suitable connections to the motor 53 and the phototube and light beam source as already described. Switching means are shown at I24 for turning 011 and on the follow-up mechanism and the amplifier, and at I25 to permit adjustment for variation in line voltage where required.

In operation the device of Figures 12 to 17 performs substantially like that of Figures 1 to 4, the operation of the follow-up mechanism itself being identical with that of Figures 1 to 4 inclusive, and the motion of the follow-up mechanism being transmitted to the recorder by moving the rack 98, and with it the pen arm I01.

Although the recorder as shown uses a straight line motion provided by the rack, it will be evident of course that any other suitable recorder motion might be employed, as well known in the art.

Suitable circuit connections for the electronic torque control unit, the phototube, the light source and the motor are shown in Figure 18, in which a suitable alternating current source, preferably at volts and 60 cycles is shown at 60 connected to a suitable amplifier 51 which is suitably connected to the phototube 54 by the leads (cable) 52, and to the motor 53 by the leads (cable) 59. The source 43 of illumination is suitably connected to 4.5 volts alternating current, and is preferably a 6. to 8 volt lamp (thus increasing the life of the lamp). The phototube is connected to the input of the amplifier 51 and the output of the amplifier is connected to a conventional motor 53, which may be operated by alternating or direct current. The amplifier 51 is designed to provide the necessary alternating or direct energizing current for the motor under the control of the phototube in accordance with well known practice.

Switches 60' are shown to disconnect the electric power and return the pen to off position, and a switch 44 is shown to short circuit the phototube and move the pen arm to the upper position in which the pen is off the chart, for chart changing.

Where an alternating current type motor is provided, an amplifier of modified character may be employed, as described and claimed in a copending application of Stephen V. Hart, Serial No. 693,792, filed August 29, 1946. While this amplifier is preferred, alternative systems are set forth below.

In Figure 19 I illustrate a suitable amplifier for performing this function when connected to :a-mre 13 ra-D. C. motor 53', which amplifier maybe that table alternating current motor ISL-of any suitof United States Patent No. 2,054,836, granted .able reversing typerespondlng to variant torque. September .22, 1936, to F. H. Shepard, for Light It =-the capacitor vtype .induction motor type is responsive device. In this construction a suit- :used, it will .be evidentthat one field connection able source of alternating current,.preferably .at I54, shunted by a capacitor .-I.54 -.will be made 6.0 cycles and 110 volts, is applied at 60 by a .to the transformer secondary 453 and the other transformer I26 having a primary I21 and sec- .,fiield connection 154 will be made directly to endary I 28 connected across a ,phototube M -,a .source of alternating current 6-0, through a through a capacitor I29. The phototube 44 is .capacitoriM normally partof the motor. monnected between the cathode I30 and control .In operation it-willbe. evident thatin this form grid I31 of an famplifier tube 132 from a series ithe direction of the motor and its operation will resistor I33 in series with the control grid. The die determined byfthe comparative outputs of the -.two ends of the resistor I33 are connected to the :two amplifiers :51 and 51 and this in turn *cathede .gmllnd y :a resistor I34 and by a :iadetermined by the quantityof light received by shunt capacitor I35 respectively. l5 ithB respectivephototubeelements -8'I and 88.

The anode I36 of amplifier I32 terminates in .In somecasesit may be preferable to oppose .connections59 to the motor 53, representing'the the impulses mechanically, a by using two sepoutput of the amplifier. The connections 59 rearate motors E55 :and 156 opposed and having a tn-m e ground through an an pp y bat- .eommon shaft 54 which iscontrolling the motion .tery 43-1. of the follow-up element of Figure 11.

In loperation 0f the deViOe o i r he If preferred, the two tphototube .units may 'D fi rectifies the pp alternating cu themselves beopposed, as-by-connecting the ret nd n o t id bias of the a p fi 'spective ;photo,tube-cathode elements 81 and 88 tube The output e t owin throu h -.by-leads-l51 and its to=the outside:terminals-of -.the motor -53 connected across the output 'term i tanoe A59, .and connecting the anod t .ininals 59 is therefore proportional .to the amount gether by .leads 450 and |5| t t center is: of light falling o the p ototube as previously -of the device. The resultant impulse across the described resistor -=I59 is 'then carried-by leads I63 .to the :In the prefer-red embodiment of the device as ,-input i r n amplifierj'Lthe t t. which already described, the motor '53 will be an alterqperates -a motor 53 desirably a capacitor type mating current motor, rather than a direct cur- .,ind p1:i n,m i-, r;a5 Shown ,Figure 2-2, rrcnt m r as sh wn at in Fi u e 9. T0 at will :be evident that various -other=circuits accomplish this function I illustrate in Figure 20 may be used 5 accomplish the power ampljfica- .a circuit substantially identical with that of Figm function w 19. but m tting th battery 1:31, mplo 5 In view of my invention and .disclosure variadditional connections at I38 .to-a source of altez=- t and odification tomeet i i al hi Hating-@111 rent, Suitably at 110 Volts 69 cycles -or :particular need will doubtless become evident mp oyin a A.-C- motor 5 As Well known to others skilled in the art, to obtain all or part in the art it will be understood that a full wave of t benefits f my invention without copyfilmlfll-ifier m ye employed i desired .40 mg the apparatus andprocess shown, and I, there- In Fi ure 2 I illustrate a circuit similar to :fore-claim all such :insofar as they fall within that of Figure .20, but designed to operate with :the reasonable spirit and scope of myclaims. --two-phase induction motor of the capacitor type, Having t described my invention t .gpreferahly a sc uirrel cage or .drag cup motor, as {claim new and .desire ,t Secure Letters .shown at 53 and preferably used in Figures l to A #P tent 10, inclusive- 1. In an .instrument,-a primary indicator :hav-

The 1110120! 53 has :a 'lOlZOl 439 :and separate jngangular-movement .ajollow-up element hazv, 19 fi d w d and Of which 1 .mg angular .movement generally conforming to is directly connected to the source of alternating t t of t =prim-ary di r, means for r flw t 6 sui y at 1: Volts 60 cyflles siectinga-beam of lightfrom a-single-source which --t u ralcapacitor While the Winding moves with the follow-up element, -means on the .-is connected-to the-output :from the amplifier I32, mflmary indicator 4' varianfly n i t a shunted y a Capaciter 4433 The amplifier beam of light from the singlesource in accord- 1 =i1= uit-= ifi rrssli h ly fr m h -0f Fi and mice with the relative angular positions of the in that the resistor 1'33 and capacitor 435 .have .primary indicators-andtheifolloweup element and "been mm-itted. I also illustrate in this form --a t g be means for continuously angularly suitable transformer M2 connected :to the alter m ,t fgllow-up m; t .primagy matin ur r upp yi th energy for :indicator shifts angularly, and in response to the p r t light extent of eclipse f the *beam -from the single Any one of a variety of circuits may be tem 80 was ..ployed with the twin photoelectric element form 2, ,.-In-an;instrument,-a primary indicator 10f Figure 1-1, and several are suggested for-con- .;ing .a,ngu1a,r ov e t, a follow-up l me t 111w.- venience. As shown inFigure ,22 the photoelecring angular movement-adapted to follow that of stric elements 81 and 88 arenorma'lly separate the primary indicator, :means for proiectinga relements cooperating w separate anodes 443 ibeam of light which-moves with the ,fOllOW-UD .and H4 in a single envelope I45. element, :means on .-the primary indicator :for .lnthe iormshownthe respective pairs of photiltliingzthe beam-oflight in one :relative angular #lmtube elements are connected by leads M6 and position with respect to the follow-up element, I41 to twin amplifiers 5'! and 51 having contorclearing the beam of light inanother-relative -nections to suitable alternating current sources angular position and for partially cutting the -60, suitably at 110 volts and cycles. "The outrbeam-in-an intermediate relative angular-position, muts 10f the respective amplifiers 'pass through a photctube responding to-the-ouantity :of light, (connections I48 and I49 to the respective rop- ,1f-any,'passing in-itheibeam, a power source for posed :primaries I50 and I5I of .a transformer thephototubaanamplifier'for the out-putsof .the ainghavingsassecondary 4'53 connected to a suit- :phototube, means {or providing a counter-torque on the follow-up element and a motor having a torque greater than the counter-torque, driving the follow-up element against the countertorque in continuous response to the amplified output of the phototube.

3. In an instrument, a primary indicator having angular movement, a follow-up element having angular movement adapted to follow that of the primary indicator, means for projecting a beam of light which moves with the follow-up element, means for producing a counter-torque on the follow-up element, means for controlling the quantity of light passed by the beam in response to the decrease of coincidence between the primary indicator and the follow-up element and means for continuously urging the follow-up element against the counter-torque by a torque responsive to the quantity of light passing in the beam and capable of exceeding the countertorque.

4. In an instrument, a primary indicator having angular movement about an axis, a follow-up element having angular movement about the same axis and adapted to follow that of the primary indicator, means for projecting a beam of light from a single source which moves with the followup element, means on the primary indicator for cutting the beam of light from the single source in one relative angular position with respect to the follow-up element, for clearing the beam of light from the single source in another relative angular position and for partially cutting the beam from the single source in an intermediate relative angular position, and phototube means for maintaining the primary indicator and the follow-up element in an equilibrium relation in which the beam from the single source is partially cut.

5. In an instrument, a, primary indicator having angular movement, a follow-up element having angular movement adapted to follow that of the primary indicator, means for projecting a beam of light from a single source which moves with the follow-up element, a vane on the primary indicator for variantly eclipsing the beam of light from the single source in accordance with the relative angular positions of the primary indicator and the follow-up element, and phototube means for continuously restoring the relative position of the primary indicator and the follow-up element which corresponds with equilibrium of the beam of light from the single source with respect to the vane.

6. In an instrument, a primary indicator having angular movement, a follow-up element having angular movement adapted to follow that of the primary indicator, means for projecting a beam of light which moves with the follow-up element, a vane on the primary indicator for cutting the beam of light in one relative angular position with respect to the follow-up element, for clearing the beam of light in another relative angular position and for partially cutting the beam in an intermediate relative angular position, a phototube responding to the quantity of light, if any, passing the vane, a power source for the phototube, an amplifier for the output of the phototube, means for providing countertorque on the follow-up mechanism, and a torque motor driving the follow-up element against the counter-torque in continuous response to the amplified output of the phototube and capable of developing torque exceeding the counter-torque.

7. In an instrument, a primary indicator including a light interfering means and adapted to turn around an axis, a follow-up element adapted to turn around the same axis, and photoelectric means including a source and a phototube mounted both on and moving with the follow-up element to return the follow-up element continuously to a balanced condition at a predetermined extent of interference by the light interfering means with the phototube as the primary indicator moves.

8. In an instrument, a primary indicator adapted to rotate around an axis, a follow-up element adapted to move preferably in coincidence with the primary indicator about the same axis, means for producing a return torque on the follow-up element of relatively low order, means for producing a light beam travelling with the follow-up element, means on the primary indicator for intercepting the iight travelling with the follow-up element and means for continuously applying a torqu opposite to the return torque and of a higher order on the follow-up element to keep the follow-up element in coincidence with the primary indicator including phototube means mounted on and carried by the follow-up element and responding to the light beam, the light to the phototube being intercepted by the primary indicator.

9. A reactionless light beam coupling comprising a rotatable primary indicator, a light intercepting vane carried by the primary indicator, a rotatable follow-up element, means mounted on the follow-up element for producing and receiving a light beam, and means for moving the follow-up element continuously to an equilibrium position in proportion to the quantity of light passing the vane.

10. A reactionless light beam coupling comprising a rotatable primary indicator having a light intercepting vane, a follow-up element adapted to rotate about the same axis as the primary indicator, means for producing a beam of light travelling with the follow-up element,

means for urging the follow-up element by a torque in one direction in response to the quantity of light passing the vane, and means for continuously producing a counter-torque of substantially half the torque, the mechanism achieving an equilibrium position corresponding to passage of approximately half of the light of the beam.

11. In an instrument, a primary indicator having angular movement, a follow-up element having angular movement adapted to follow that of the primary indicator, means for projecting a beam of light from a single source in a single direct straight path which moves with the follow-. up element, means on the primary indicator for cutting the beam of light from the single source along its single direct straight path in one rela-. tive angular position with respect to the followup element, for clearing the beam of light from the single source in another relative angular position and for controllably and partially cutting the beam from the single source in an intermediate relative angular position, and phototube means for continuously maintaining the primary indicator and the follow-up element in the relation in which the beam from the single source is partially cut and the primary indicator and the follow-up element are in equilibrium.

12. In an instrument, a primary indicator having angular movement, a follow-up element having angular movement adapted to follow that of the primary indicator, a light source mounted on and moving with the follow-up element and projecting a beam of light which moves with the 137 Hollow-up element, means-on the.- prlmaryindieartor :forxuttingnthe beam :of light in one reiati-ve :eanglflar-mosition with respect .tO the 'ffollow-rup -;-.element-;.for:;ciearing the beam ofllight in another #18 :zbeing respeotlvely'one nearer to: and one farther lifrom thea-xis of :the :followup =element.

11i. In aninstrument aprimary-indicator having angularmo vementabout-an -axis,- a followmelative angularposition and for. partiallyxcutting-,-,-5 "up element-havlng angular-movement about the s the. heaamin an intermediate equilibrium: position, 1:2. phototube-mounted on sand -moving with sthe r'foliowsup; element and; responding to the quantity eofJlShtJltany, passinglin theoeam, a power -.-output sof.:.thephototube, means for providinga reonnterstorque son the I follow-up element and: a

twztorque motor ncapable of .developing torque taxmeeding thelcounter torqueand drivlngthe foli-iiowsup relement against the counter-torque in montinuousz-response to the amplified output :of

the phototube.

":13. .Inaniinstrument, a primary indicator hav- 'ing angular movement, affollow-up element havaingangular-movement adapted to follow zthatoof zthe aprimary :indicator, =a recorder :moved con- :ctinuously lin response-=to the movementiof the 21f ollow-up element, means 1 for projecting a: beam sunlight which moveswith thafollow up element, means won .:the primary-indicator for var-iantly reclipsingithe beam of light in accord-ancerto the welative angular positionsoithe: primary indicamtor mnd thefollcw-up element, and phototube 'rmeansifor continuously :angularly shifting :the followwp element "and I thereby the recorder -as =-=the :primary indicator :shifts angularly, and in .-rresponsezto extent'of eclipsing of the beam.

14. In an. instrument, a primary indicator hav- --ing-. angularanovement, affollow-up element having angular movement adapted to 'follow that-of t the=prim=ary indicatona recorder continuously :moved in: response: to the movement ofthe follow- .zup-element, means forprojecting a beam of-light =;which;moves with the follow-up element, means :on "the-primary indicator for cutting the beam 0ft light: in one-relative angular position with reaspect to the follow-up element, for-clearing the beam o'f light in another relative angular position and 'for partially cutting --the beam -in-=an *intermediateequilibrium position, a -phototube -Pespondingto the-quantity of light, if---any,'pass-' ing in the beam; a powersourcefor-the phototube, 'an-amplifier for -the output -of the phototube,

means for providing continuous countertorque onthefollowmp element, and a torque motor capable-of developing torque exceeding-the coun-- *ter-torque and moving the'follow-upelement and "the recorder continuously against thecounter-i torque incontinuous response to the amplified output of 'the phototube.

115. In an instrument, a, primarytindicatorlhavingangular movement on an axis, .a -followenp element .having angular movement about .the same axis and adapted to followethe movement same axis and "adapted tofollow 1 the movement -ofithe primary indicator a light source-mounted on and =-moving with the l'ollow -up element -for projecting-a beam of lightwhich moves with'the ssourcezfor-"the phototube, annamplifierv ifor cthe foliow up elementa'vane on the primary indioator for' cutting-Athe beamof light inone-=relative angular position with respect to the follow-up element, for clearing the beam of light in I an- --otherrelative=-angular position :and for partially cutting'the beam i in an intermediate equilibrium "position; a =phototube :mounted --on and moving --avith=the follow-up element beyond the vane and respondin-g to the -quantity of light, if=any,-passing in the beamgthe-light source and phototube being positioned vrespectively one nearer to and -one farther= from '-the-'axis,-' a-power-sourcefor the phototube, -an=. amplifier -=for the output of the :phototuba'means-ior providing a counter=torque -on --the =follow-up element and a torque motor 'eapa-ble --of developing torque which exceeds -*the "counterelm-qua and driving the'follow -up element "against the counter torque in continuous response "-tothe amplified output of the-phototube.

17. in-andnstrument, a-primary indicator'hav- 130' *ing angularmovement, a follow-up element hav- "ing angular movement about the :same-axls-as the primary indicator and-adapted 'to fcllow'the "movement "of the-;primary -indicator, a light source -mounted on-and moving wlththefollowzlfiup element forpm ecting--a*beam of light gen- -eraliyqsla'rallel to the radius and-moving with-the follow-upeiement; an-elongatedvane having-substantial =r-adial l-ength-cn the primary indicator *and mcving into the path of-thebeammf-light :iIl-OHG relative angular "position i with respect-to the-'folloW-upelement;clearing the beamof light *nt'ancther relative angular position-andpartially cutting the beam at an-intermediate equilibrium "position, a phototube mounted onand moving 5 with the followup-elementbeyond thevane and responding to-the-quantity ofl-ight, if'any,-pass- 1 ing in the beam, 2: powersource for the phototube, an amplifier'for the output-of the phototube,

means for providing counter-torque on thefollowon 'up element *and *a torque motor -capable of de- 'velopingtorque excee'dingthe counter-torque-and driving the follow-up element 4 against the counter-torque-in-oontlnuous response to 'the amplifle'd -output-of the phototube.

o5 1'8.-Inan instrument, a primaryindicator having angular movement;a followup-element hav- 'ing angular movement about the same "axis :as "the'primaryindicator,-and-adapted to'foll-ow the movement ofthe primary indicator, ailight source {of theprimaryindicator, a singlerlight eowmounted-ontheiollow-upelement-at a distance ,=mounted .omand moving with the follow-up ele-' ment-ior projecting a .beam of light which moves with thefollow-up element, a vane on the primary indicator-for variantly eclipsing the beam of light ifromlthezsingle-source in accordance withrthe srelative ,ariguiarg-positions of the. primary indicaitor'and "the follow-up element, and -phototube ;means, :including aphototube mounted-on :the-

*fmmthe-axisand'projecting a beam of light rgenerallytoward the-axis,-a vane-onthe primary 'lndicatormearer the axis than the light --source aor cutting the beam of light'in---one-relative angular position "with '-respect to the "follow up elementFforclearing-the beam-of light in another relative :angularlpositicn and for-partially cutting the beam -in an intermediate --relative angular rposition, a *phototube mounted on the follow-up -f ll -1lp-.element beyond the vanezand'moving im element on the --opposite side obtheaxis mm "with the -follow.-np element, for -.contim1o.u sly angularly shifting the follow-up element asrthe primary indicator :'shifts ;.angularly, and in .ressponsezrtorthegextent of eclipse of the beam from 'the source-and responding to the quantity of flight, 'if anmuwhioh passes the vane, -a power ssource the photctube, an amplifier for the mutput of' the -phototube, means for providing --.-tbe:-sing1e;somce;. thelightsource and phototube s15 rewrites-torque on the'ifollow upelement, and -a motor capable of developing torque exceeding the counter-torque and driving the follow-up element against the counter-torque in continuous response to the amplified output of the phototube.

19. In an instrument, a primary indicator having angular movement, a follow-up element having angular movement about the same axis as the primary indicator, and adapted to follow the movement of the primary indicator, a light source mounted on the follow-up element at a distance from the axis and projecting a beam of light generally toward the axis, a vane on the primary indicator nearer the axis than the light source for cutting the beam of light in one relative angular position with respect to the followup element, for clearing the beam of light in another relative angular position and for partially cutting the beam in an intermediate relative angular position, a phototube mounted on the follow-up element on the opposite side of the axis from the source and responding to the quantity of light, if any, which passes the vane, a phototube having a photo-sensitive element substantially out oi the line of centers between the phototube and the axis, a power source for the phototube, an amplifier for the output of the phototube, means for providing counter-torque on the follow-up element, and a motor capable of developing torque exceeding the counter-torque and driving the follow-up element against the counter-torque in continuous response to the amplified output of the phototube.

20. In an instrument, a primary indicator having angular movement, a follow-up element having angular movement generally conforming to that of the primary indicator, means for projecting a beam of light from a single source generally parallel to the radius and which moves with the tollow-up element, a segmental vane on the primary indicator for variantly eclipsing the beam of light from the single source in accordance with the relative angular positions of the primary indicator and the follow-up element and phototube means responsive to light passed by the segmental vane for continuously angularly shiftingthe follow-up element as the primary indicator shifts angularly, and in response to the extent of eclipsing of the beam from the single source.

21. In an instrument, a primary indicator having angular movement, a follow-up element having angular movement adapted to follow that of the primary indicator, means for projecting a beam of light in a general direction parallel to the radius and which moves with the follow-up element, a segmental vane on the primary indicator for cutting the beam of light in one relative angular position with respect to the followup element, for clearing the beam of light in another relative angular position and for partially cutting the beam in an intermediate equilibrium position, a phototube responding to the quantity of light, if any, passed by the vane, a power source for the phototube, an amplifier for the output of the phototube, means for providing counter-torque on the follow-up element and a motor capable of developing torque exceeding the counter-torque and driving the follow-up element against the counter-torque in response to the amplified output of the phototube.

22. In an instrument, a primary indicator having angular movement, a follow-up element having angular movement adapted to follow that of the primary indicator, means for projecting a beam of light generally parallel to the axis and which moves with the follow-up element, a vane extending in a plane transverse to the axis of the primary indicator and mounted thereon for cutting the beam of light in one relative angular position with respect to the follow-up element, for clearing the beam of light in another relative angular position and for partially cutting the beam in an intermediate relative angular position, a phototube responding to the quantity of light, if any, passing the vane, a power source for the phototube, an amplifier for the output of the phototube, means for providing counter-torque on the follow-up element and a motor capable of developing torque exceeding the countertorque and driving the follow-up element against the counter-torque in continuous response to the amplified output of the phototube.

23. In an instrument, a primary indicator having angular movement, a follow-up element having angular movement generally conforming to that of the primary indicator, means including a single source for projecting a beam of light which moves with the follow-up element, means on the primary indicator for variantly eclipsing the beam 01' light in accordance with the relative angular positions of the primary indicator and the follow-up element, and phototube means including two phototube elements operating on the beam from the single source for continuously angularly shifting the follow-up element as the primary indicator shifts angularly and in response to the extent of eclipse of the beam with respect to either phototube element.

24. In an instrument, a primary indicator having angular movement, a follow-up element havin angular movement adapted to follow that of the primary indicator, means including a single source for projecting a beam of light which moves with the follow-up element, means on the primary indicator for cutting the beam of light in either direction, phototube means including two phototube elements operating on the beam from the single source responding to the quantity of light passed in the beam to the respective elements, a power source for the phototube means, amplifier means for the outputs of the phototube means and motor means driving the follow-up element in response to the relative amplified outputs of the phototube means. a a

25. In an instrument, a primary indicator having angular movement, a follow-up element having angular movement generally conforming to that of the primary indicator, photo-responsive means for driving the follow-up element in continuously balanced relation to the primary indicator, a recorder having a pen driven by the follow-up element and means cooperating with the photo-responsive means for moving the recorder to a limiting position and concurrently removing the pen from the record.

26. The process of controlling the following of an angularly movable primary indicator by an angularly movable follow-up element, which comprises projecting a beam of light from a single source which moves with the follow-up eleme'nt, variantly eclipsing the beam of light from the single source in accordance with the relative angular relationship of following, and continuously progressing the follow-up element as the primary indicator shiits angularly, and in response to the extent of the eclipse of the beam from the single source.

27. The process of controlling the following oi an angularly movable primary indicator by an angularly movable follow-up element, which comprises projecting a beam of light which moves with the follow-up element, variantly eclipsing the beam of light in accordance with the relative angular relationship of following, and continuously progressing the follow-up element as the primary indicator shifts angularly, and against a counter-torque, by a torque responsive to the extent of eclipse of the beam.

28. The process of controlling the following of an angularly movable primary indicator by an angularly movable follow-up element, which comprises projecting a beam of light which moves with the follow-up element, variantly eclipsing the beam of light in accordance with the relative angular relationship of following, and continuously progressing the follow-up element as the primary indicator shafts angularly, and against a counter-torque, by a torque responsive to an amplified photoelectric impulse from the quantity of light in the beam.

29. The process of controlling the following of an angularly movable primary indicator by an angularly movable follow-up element, which comprises projecting a beam of light from a single source which moves with the follow-up element, cutting the beam from the single source by the primary indicator in one relative angular relationship of following, passing the beam from the single source in another relative angular relationship and partially cutting the beam from the single source in an intermediate relative angular relationship, and continuously restoring the follow-up element to the relationship in which the beam is partially cut by an amplified photoelectric impulse responding to the quantity of light in the beam from the single source.

30. The process of controlling the following of an angularly movable primary indicator by an angularly movable follow-up element, which comprises pivoting the primary indicator and the follow-up element on the same axis, projecting a beam of light from a single source which moves with the follow-up element, variantly eclipsing the beam of light from the single source in accordance with the relative angular relationship of following, and continuously progressing the follow-up element as the primary indicator shifts angularly to restore the initial extent of the eclipsing of the beam from the single source.

31. The process of controlling the following of an angularly movable primary indicator by an angularly movable follow-up element, which comprises projecting a beam of light which moves with the follow-up element, variantly eclipsing the beam of light in accordance with the relative angular relationship, and continuously progressing the follow-up element as the primary indicator shifts angularly, against a counter-torque, by a torque responsive to the quantity of light passed in the beam, to restore equilibrium with respect to illumination conditions.

32. The process of controlling the following of an angularly movable primary indicator by an angularly movable follow-up element, which comprises projecting a beam of light which moves with the follow-up element, variantly eclipsing the beam of light in accordance with the relative angular relationship, and continuously progressing the follow-up element as the primary indicator shifts angularly against a counter-torque, by a torque responsive to an amplified photoelectric impulse from the quantity of light in the beam, to restore continuously the initial equilibrium conditions with respect to illumination.

33. The process of controlling the following of an angularly movable primary indicator by an angularly movable follow-up element, which comprises projecting a beam of light from a single source which beam moves with the follow-up element, variantly eclipsing the beam of light in accordance with the relative angular relationship, and continuously progressing the follow-up element as the primary indicator shifts angularly, by a torque responsive to amplified balanced photoelectric impulses from the quantity of light in the beam from the single source.

34. The process of maintaining angular positional relationship between a primary indicator having a vane and a follower having a single phototube mounted thereon, which comprises photoelectrically controlling the angular follower response entirely in accordance with change in the degree of shading by the vane upon the single phototube.

35. The process of manipulating a follower in response to a primary indicator moving about a. common axis of rotation, which comprises modulating a light beam from a single source moving with the follower by the action of the primary indicator and controlling the motion of the follower photoelectrically to restore equilibrium at a predetermined extent of modulation of the beam from the single source.

WALTER J. KINDERMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,154,438 Rose Sept. 21, 1915 1,585,210 Roux May 18, 1926 1,589,673 Winter June 22, 1926 2,189,802 Karlsson-Ygger Feb. 13, 1940 2,360,399 Chandler- Oct. 1'7, 1944 2,370,000 Best Feb. 20, 1945 2,391,123 Carliss et al Dec. 18, 1945 FOREIGN PATENTS Number Country Date 605,820 France June 2, 1926 

